The invention relates to an evaluating unit for a device for detecting objects, in particular for monitoring the interior of a motor vehicle. The invention also relates to a device for detecting objects, in particular for monitoring the interior of a motor vehicle, having an evaluating unit. The invention further relates to a method for controlling a device for detecting objects, in particular for monitoring the interior of a motor vehicle.
In exceptional situations, occupant protection devices such as airbags can not only protect occupants of a vehicle against the health consequences of collision, but can also constitute a risk for the occupants. For example, if an occupant assumes in his vehicle seat a position which is unusually close to the dashboard, and a collision occurs, the head, in particular, of the occupant is struck with the full force of the airbag owing to the sudden inflation of the latter. In these circumstances, the risk of injury by the airbag is greater than its protective effect. A small child in a child seat is also exposed to just this risk of injury, in particular when the child seat is disposed on the passenger seat with its back rest facing the dashboard (reboard child seat). Thus, if an occupant or a child seat has too small a spacing from an exit opening of the airbag, the airbag is not to be activated, or is to be activated only to a reduced extent.
On the other hand, it is advantageous to be able to distinguish an occupied vehicle seat from a non-occupied one, in order to prevent the triggering of the occupant protective device assigned to the vehicle seat. Unnecessary repair costs for exchanging an airbag unit as a consequence of the unnecessary triggering can be avoided by an appropriate device for detecting objects, in particular for detecting an occupant or a child seat.
A known device for detecting a child seat in a motor vehicle (see Published, European Patent Application EP 0 708 002 A1) has a transmitting antenna and two receiving antennas which are fitted in the vehicle seat. An evaluating unit excites the transmitting antenna with a carrier signal to emit an electromagnetic field. A child seat disposed on the vehicle seat has two resonators/transponders, which characteristically vary the electromagnetic field generated by the transmitting antenna. The receiving antennas, magnetically coupled to the transmitting antenna, receive the measuring field characteristically varied by the resonators in the child seat, and supply the carrier signal modulated in this way to the evaluating unit as an input signal. The evaluating unit includes a demodulator that demodulates the input signal. By evaluating the useful signal thus obtained, an evaluator detects whether a child seat is disposed in the surroundings of the vehicle seat or not.
In the event of nondetection of a child seat, the demodulator preferably supplies a useful signal without characteristic properties, in particular a zero signal, since the carrier signal emitted by the transmitting antenna is coupled on to the receiving antenna without being modulated. The demodulation of this unmodulated carrier signal normally supplies a zero signal. However, if, for example, the transmitting antenna or the receiving antenna, the demodulator itself or a component disposed between the receiving antenna and demodulator is defective, the demodulator likewise supplies a zero signal which is interpreted by the evaluator as a child seat which is not present.
It is accordingly an object of the invention to provide an evaluating unit for a device for detecting objects, in particular for monitoring the interior of a motor vehicle, as well as a device for detecting objects having such an evaluating unit and a method for controlling such a device which overcome the above-mentioned disadvantages of the prior art devices and methods of this general type, which device/method is capable of reliably distinguishing a defect from an object which is not detected.
With the foregoing and other objects in view there is provided, in accordance with the invention, an evaluating unit for a device for detecting objects, including:
a demodulator receiving an input signal and a carrier signal and deriving a useful signal from the input signal with the aid of the carrier signal, the demodulator generating a modulated carrier signal modulated with an auxiliary signal and deriving a test signal from the input signal with the aid of the modulated carrier signal; and an evaluator receiving the useful signal and the test signal, the evaluator detects a presence of an object by evaluating the useful signal and detects a malfunction by evaluating the test signal.
In addition to deriving the useful signal from the input signal, supplied to the evaluating unit, with the aid of the carrier signal, the demodulator is also configured to the effect that the input signal can be demodulated with the aid of the carrier signal, modulated with an auxiliary signal, in order to derive a test signal. The evaluator downstream of the demodulator evaluates the useful signal and/or the test signal. The evaluator detects the presence of the object by evaluating the useful signal. The evaluator also detects a malfunction by evaluating the test signal.
In an alternative embodiment, a receiving antenna is provided which supplies the input signal to the previously described evaluating unit according to the invention.
In a method for operating the device, the carrier signal is emitted via a transmitting antenna of the device. The carrier signal is modulated with an object-specific signal by the object to be detected. The modulated carrier signal is received as the input signal by a receiving antenna coupled to the transmitting antenna. The input signal is demodulated with the carrier signal, the object being detected when the input signal demodulated with the carrier signal includes the object-specific signal. The input signal is demodulated with the carrier signal modulated with an auxiliary signal when the input signal demodulated with the carrier signal does not include the object-specific signal. A malfunction is detected when the input signal demodulated with the modulated carrier signal does not include the auxiliary signal.
The advantage of the invention resides in that an object not detected can be distinguished from a defect in the evaluating unit or the device, if the defect relates to one of the components of the device upstream of the evaluator, that is to say the antennas or the demodulation circuit, in particular. If the result of the evaluation of the useful signal is that it does not include any signal shape characteristic of an object, that is to say any object-specific signal, in a further step the input signal of the evaluating unit is demodulated with the carrier signal which is, however, now for its part modulated. If the auxiliary signal with which the carrier signal was modulated is detected by the evaluator in the test signal formed in such a way, the system is not defective. At the same time, no object is detected. In this case, the input signal corresponds to the carrier signal which is subsequently demodulated with the aid of the modulated carrier signal, with the result that the modulating signal, precisely the auxiliary signal, is detected in the test signal. However, if the auxiliary signal is not detected in the test signal, a defect is present in the device. For example, the receiving antenna is broken, with the result that the input signal is equal to a zero signal.
Depending on the evaluation of the test signal, the evaluator emits output signals which can be distinguished from one another. The invention also permits a device defect to be checked without a large outlay on circuitry. Thus, there is no need for current or voltage measuring devices. A defect can be detected solely by controlling the demodulator and by the evaluation, possibly in terms of software, of its output signal.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an evaluating unit for a device for detecting objects, in particular for monitoring the interior of a motor vehicle, as well as a device for detecting objects having such an evaluating unit and a method for controlling such a device, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.